1. Field of the Invention
The present invention relates to an apparatus for actively suppressing vibration or noise.
2. Description of the Related Art
JP-A-2000-330572 (PTL 1) and JP-B2-3572486 (PTL 2) mention that a transfer function of a secondary path (a secondary transfer function) is determined beforehand, an adaptive filter coefficient is updated by using this determined function as a feedforward coefficient, and a control signal is generated by using the adaptive filter coefficient. Examples of this kind of algorithm include a Filtered-X Least Mean Squares (LMS) algorithm. Besides, JP-B2-4742226 (PTL 3) describes a direct adaptive algorithm capable of updating an adaptive filer coefficient of a control signal without determining a secondary transfer function.
Moreover, the above PTL 1 mentions that in cancelling road noise in a vehicle interior, updates of the adaptive filter coefficient of the control signal are carried out while a vehicle idles and are not carried out while the vehicle runs. JP-A-2011-43636 (PTL 4) describes switching between generating a control signal while updating the filter coefficient of the control signal by a simultaneous equation method and generating the control signal by using the stored filter coefficient.
[PTL 1] JP-A-2000-330572
[PTL 2] JP-B2-3572486
[PTL 3] JP-B2-4742226
[PTL 4] JP-A-2011-43636